Pushbuttons of this kind are generally used to input commands to so-called machine/man interfaces. It is feasible to use the pushbuttons not only to switch control currents but also to switch power by the pushbutton being used as a trigger for circuit breakers. These pushbuttons are subject to high demands in respect of service life, robustness, sealing off the electrical part from water and dirt and also the ability to be produced in as cost-effective a manner and with as reliable a process as possible.
Command devices are fitted in switch panels, control panels, switchgear cabinet doors or housing covers. Command devices are generally of modular construction. This means that they comprise an actuator, a fastening part such as an annular nut or a mounting holder for example, and one or more switching elements which are designed as break-contact or make-contact switching elements. For assembly purposes, the actuator is generally guided, from the front, through a hole in the switch panel and fitted from the rear by means of a fastening part. The switching elements are mechanically fastened to the actuator or to the fastening part by screws, snap-action hooks or bolts. The switching elements are electrically connected to the control system by means of connection terminals.
In safety applications such as, for example, emergency-off command devices, it is stipulated that the signal be generated by virtue of positive-opening contacts being opened. This means that, if an emergency-off command device has not been actuated, the contacts, and thus the associated electrical circuit, are closed. In the event of disruption or an emergency, the break contact is broken as a result of the emergency-off actuator, which is located in front of the switch panel, being struck, and the system or machine is put into a safe state. However, this works only when the spatial arrangement of the actuator and switching element is ensured. Defective assembly or the exertion of force may result in the switching elements being mechanically separated from the actuator. In this case, the emergency-off command device is no longer functional, that is to say, upon actuation in the event of an emergency, the contacts are not opened, and therefore the hazard state cannot be eliminated. This may have fatal consequences for man and machine. A considerable amount of importance is therefore given to the reliable connection between the actuator and switching element.
In particular, the actuators have to meet complex requirements. They should, for example, be easy to fit and be as attractive as possible to the customer. The principle for each actuator is that it forwards defined switching position information and maintains the switching position. In the case of the emergency-stopping command device product group, it is particularly important to maintain the switching position so that the safety circuit is prevented from switching on again. In order to ensure this function, it is necessary to fit the locking mechanism securely in the collar.
Different structural and assembly-related solutions have been used in order to ensure functioning. For example, in specific actuators, for example emergency-stopping actuators, the functional components are individually supplied and checked, and the entire assembly is tested after assembly. Other variants hold the individual pre-fitted assemblies in position by means of fitting apparatuses, as a result of which it is subsequently necessary to test the functioning and check individual components.